There are many applications which require fast switching speeds. For example, for multi-mode multi-band cell phone applications such as GSM (Global System for Mobile Communications), GPRS (General Packet Radio Service), and 3G (Third Generation Wireless), the antenna switch unit switches the antenna to different bands as well as between transmission (TX) and receiving (RX) modes. Currently, solid-state switches are used for this purpose. While RF (Radio Frequency) MEMS metal contact series switches generally have much better insertion loss and isolation characteristics, they are much slower than solid-state switches.
Referring to FIGS. 1 and 2, these figures illustrate a top view and a side view of a MEMS in-line cantilever beam metal contact series switch, respectively. This type of MEMs switch can be manufactured by well known MEMS fabrication processes.
As shown, the switch is formed on a substrate 100 having an isolation layer 101. A metalized signal line 102 may be formed on one side of the substrate 100 and a second signal line 104 may be formed on the second side of the substrate 100 over the isolation layer 101. A cantilevered beam 106 may be secured to the second signal line 104 with an anchor 103. A bump (electrode) 108 may be formed for example by a field oxide (FOX) technique under the first signal line 102. A lower electrostatic actuation plate 110 may be formed on the substrate 100 beneath an upper electrostatic actuation plate 111 formed in the cantilevered beam 106. When the actuation plate 110 is energized, by applying a voltage, the upper actuation plate 111, and thus the cantilevered beam 106, is pulled downward causing the bump 108 with the first signal line 102 to make contact with the cantilevered beam 106. This closes the switch and provides an electrical signal path between the first signal line 102 and the second signal line 104.
Referring to FIG. 3, the most common switch failure is a short between the upper 111 and the lower electrostatic plates 110. Such shorts can occur due to deformation of the upper beam 106. The most common deformation is typically due to torque that creates short between the corner of the upper electrode 111 and the lower electrode 110. As shown in FIG. 3, the corner of the upper electrode exhibits signs of torque related shorts 120.